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Recovery of vanadium during ammonium molybdate production using ion exchange
Hydrometallurgy 104 (2010) 317–321
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Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Short communication
Recovery of vanadium during ammonium molybdate production using ion exchange Xuewen Wang ⁎, Mingyu Wang, Lihua Shi, Jian Hu, Peng Qiao School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 27 April 2010 Received in revised form 19 June 2010 Accepted 20 June 2010 Available online 26 June 2010 Keywords: Molybdenum Vanadium Separation Recovery Ion exchange
a b s t r a c t The recovery of vanadium in ammonium molybdate production with raw sodium molybdate solution was studied. Experimental results showed that the vanadium and some of impurities P, As and Si can be adsorbed along with the molybdenum from the feed liquid by the weak base resin D314 in the pH range of 2.5–3.5 and then they can be eluted from the loaded resin with ammonia liquor. The vanadium can partially naturalprecipitate from the eluted solution. The lower the pH value is and, the longer the standing time is, the less the vanadium remained in the solution will be. Standing for 24 h in pH value 6.9, the vanadium in the solution was reduced to 0.51 g/L V2O5. It was found that the precipitate is ammonium isopoly-vanadate and it is impure. By washing the precipitate with hydrochloric acid and ammonia solution sequentially and then roasting at 500 °C for 2 h, the product of V2O5 with the purity 99.12% was obtained. The impurities P, As and Si in the stood solution were removed by purifying with MgCl2 under the pH value range of 8.0–9.0 at 60–80 °C for about 2 h, while the removal of the vanadium in the solution was performed by adsorbing with the strong base resin D296 in pH value about 7.0. The devanadiumized solution can be used to produce high-quality ammonium molybdate. The loaded vanadium resin was eluted with HCl 6 mol/L and, the eluted solution was returned to adjust the sodium molybdate solution pH value. The vanadium can be effectively separated and recovered in the process. © 2010 Elsevier B.V. All rights reserved.
1. Introdution Due to numerous co-properties in chemistry of molybdenum and vanadium, it is relatively more difficult to separate and recover vanadium from molybdate solution. In ammonium molybdate production, if the average vanadium concentration is more than 0.01 g/L V2O5 in the ammonium molybdate solution, the ammonium molybdate crystal formed by adding nitric acid in the solution will be yellow, and the content of vanadium is commonly above 0.0015% in the yellow crystal. The color is not natural for the molybdenum oxide obtained by calcining the yellow crystal at about 350 °C. The molybdate solution which containing vanadium, commonly referred to the leaching solutions of dead catalyst from petroleum-refining industries for hydrogenation processes, Ni–Mo ore, high impurity Ni– Mo–Fe alloy and so on, has become one of the principal raw materials for the production of ammonium molybdate in China (Shi and Wang, 2004; Hu et al., 2006; Wang and Wang, 2010; Wang et al., 2007). In the leaching solution, the vanadium (V) is in the form of VO− 3 at the pH value over 8.0 and, the VO− 3 changes into isopoly-vanadic acid anion with the pH value decrease from 8.0 to 2.5, then the isopoly-
⁎ Corresponding author. E-mail address: [email protected] (X. Wang). 0304-386X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2010.06.012
vanadic acid anion transforms into VO+ 2 when the pH value is less than 2.5 (Zhang, and Shen, 1991). The molybdenum (VI) in the solution is in 2− the form of MOO2− 4 at the pH value over 6.5 and, the MOO4 changes into isopoly-molybdic acid anion with the pH value decrease from 6.5 to 2.5, then the isopoly-molybdic acid anion partial transforms into MoO2+ 2 when the pH value is less than 2.5 (Zhang and Zhao, 2005; Baes and Mesmer, 1976). Therefore, the molybdenum and the vanadium in the feed solution can be simultaneously adsorbed by weak base resin at the pH range from 2.5 to 6.5 and, after eluting the loaded resin with ammonia solution, the ammonium molybdate solution containing vanadium can be obtained (Hu et al., 2009). To produce pure ammonium molybdate, many methods, such as ammoniate precipitation (Chen et al., 2004; Biswas et al., 1985; Luo et al., 2004), solvent extraction (Neková and Schrötterová, 2000; Zhang et al., 1996; Komasawa et al., 1987) and ion exchange (Hu et al., 2009; Henry and Van Lierde, 1998; Hirai and Komasawa, 1993; Li et al., 2009), have been used to remove vanadium from molybdate solution, while the recovery of vanadium was commonly overlooked, which resulted in not only vanadium resource uneconomicalness but also environmental pollution in ammonium molybdate production. The present investigation deals with the application of ammoniate precipitation and ion exchange to separate vanadium from ammonium molybdate solution and to obtain purified ammonium metavanadate by using hydrochloric acid and ammonia solution to decontaminate for the vanadium precipitate.
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was decontaminated with hydrochloric acid and ammonia solution and then roasted to obtain vanadium pentoxide.
2. Experimental methods 2.1. Materials and analysis
3. Results and discussion The sodium molybdate solution used to produce ammonium molybdate was obtained from Qinghe Huanqiu Chemical Plant, which was produced by roasting high impurity ferromolybdenum powder with sodium carbonate in air and leaching the calcined powder with water (Wang et al., 2006). The composition of the solution was shown in Table 1. Hydrochloric acid, ammonia liquor, magnesium chloride, distilled water, weak base anion exchange resin D314 and strong base anion exchange resin D296 were used in the experiments. The resins were obtained from Hangzhou Zhengguang Chemical Company. Molybdenum was determined with ammonium thiocyanate colorimetry by spectrophotometer, vanadium was titrated with ammonium ferrous sulfate (Chemistry Department, 1982). Arsenic, phosphorus and silicon was determined by chemical methods and inductively coupled plasma emission spectroscopy (ICP) with a PS-6 PLASMA SPECTROVAC, BAIRD (USA). The pH was determined with ORION-230A which was made in USA, the degree of accuracy is 0.01.
Fig. 2 is the relationship of feed liquid pH value and Mo operating adsorption capacity of the resin D314 and the V concentration in the effluent at the breakthrough point of 0.1 g/L Mo. Fig. 2 shows that the resin adsorption capacity for molybdenum increases with the pH value decrease from 5.23 to 2.72, then the adsorption capacity decreases with pH value decrease. The resin has a maximal operating adsorption capacity of 142.8 g/L at pH 2.72. The adsorption capacity is 100.3 g/L at pH 1.72, which is close to the adsorption capacity 107.6 g/L at pH 3.57. To outward seeming, this is contrary to the form of the molybdenum (VI) existing in the solution. Fig. 3 is the adsorption curve of the resin D314 for molybdenum at pH 1.72. Fig. 3 shows that the pH value in the effluent is higher than that in the feed liquid, which indicates that the adsorption can promote MOO2− 4 condensation (Zhang and Zhao, 2005).
2.2. Experimental procedure
2 RCl + 2H + 2MoO4
The resins were respectively first soaked in distilled water for 24 h, and then alternately soaked in NaOH 2 mol/L and HCl 2 mol/L for 2 h, repeated three times as this way, at last activated with HCl 2 mol/L and rinsed with distilled water before use. Trials for the sodium molybdate solution ion exchange with the resin D314 were carried out in a glass column ϕ2.0 × 40 cm which operated with the pH value adjusted solution at the temperature 25 ± 0.5 °C. Forty (40) milliters of the resin was wet-packed into the glass column. The operation was performed by downstream flow at a constant flow rate of 40 ml/h. Samples were collected periodically from the column effluent and analyzed to determine vanadium and molybdenum content. The loaded resin was eluted with NH3·H2O 6 mol/L and regenerated with HCl 2 mol/L by downstream flow at the flow rate of 40–80 ml/h. The separation of vanadium from ammonium molybdate solution with the resin D296 was carried out in a glass column ϕ2.0 × 32 cm which operated with the purified solution at the temperature 25± 0.5 °C. Thirty (30) milliliters of the resin was wet-packed into the glass column. The operation was performed by downstream flow at a constant flow rate of 30 ml/h. Samples were collected periodically from the column effluent and analyzed to determine vanadium and molybdenum content. The loaded resin was eluted and regenerated with HCl 6 mol/L by downstream flow at a constant flow rate of 30 ml/h. The separation and recovery of vanadium in ammonium molybdate production were performed according to the flow sheet as shown in Fig. 1. To increase the resin D314 adsorption capacity, the pH value of the sodium molybdate solution was adjusted with hydrochloric acid, or the vanadium eluted solution and the ammonium molybdate crystal mother liquor (see Fig. 1). After adsorption, the molybdenum and the vanadium loaded on the resin was eluted with ammonia liquor. The pH value of the eluted solution was adjusted with hydrochloric acid to make the vanadium precipitated. To remove the impurities P, As and Si, the eluted solution was purified with MgCl2. The vanadium remained in the purified solution was further removed by adsorbing with the resin D296. The vanadium loaded on the resin was eluted with hydrochloric acid. The vanadium precipitate Table 1 Composition of the solution obtained by leaching the calcined ferromolybdenum powder with water, g/L. Mo
V2O5
P
As
SiO2
pH
22.42
2.48
5.21
0.27
7.28
9.76
3.1. Vanadium adsorption
P
þ
P
þ
2−
= R4 Mo4 O13 + 2Cl
P
þ
2−
+ MoO4
2−
4RCl + 2H + 2Mo2 O7 6RCl + 2H + 3Mo2 O7
P
−
+ H2 O
ð1Þ
−
ð2Þ
= R2 Mo2 O7 + 2Cl P
2−
+ H2 O
P
−
= R6 Mo7 O24 + 6Cl
+ H2 O ð3Þ
From Fig. 2 it can be seen that Mo adsorption capacity decreases markedly when the feed liquid pH value is higher than 3.5, while the V concentration in the effluent increases evidently if the feed liquid pH value is less than 2.5, which indicates the optimal pH value range for the resin adsorbing molybdenum and vanadium from the solution should be from about 2.5 to 3.5. 3.2. Vanadium separation and recovery The molybdenum and the vanadium can be eluted from the loaded weak base resin with ammonia liquor. The composition of the eluted solution is listed in Table 2. It was found that the vanadium can partially natural-precipitate from the eluted solution and, the precipitation depends on the pH value as well as the standing time. Ammonium vanadate precipitate can be formed in the solution containing vanadium (V) by adding ammonium salt (Zhang, and Shen, 1991). In fact, the eluted solution is the mixed solution of ammonium molybdate, ammonium vanadate and ammonium chloride. Fig. 4 is relationship of the standing time and the vanadium concentration in the solution, which was adjusted the pH value from 9.55 to 7.42 with HCl 6 mol/L at room temperature. Fig. 4 shows that vanadium precipitation in the solution is close to balance after standing for 24 h at pH 7.42. The compositions of the vanadium precipitate and the stood solution after standing for 24 h are listed in Table 2 as well. Fig. 5 is the vanadium concentrations in the solution in different pH value after standing for 24 h at room temperature. From Fig. 5, it can be seen that, in the pH value range of 9.5–6.9, the lower the pH value is, the less the vanadium remained in the solution will be. After standing for 24 h in pH 6.9, the V2O5 in the solution was reduced to 0.51 g/L. With HCl addition, the pH value decreases, the form of the vanadium existing in 4+ the solution becomes HV2O2+ 7 and V4O12 (Zhang, and Shen, 1991) and, + the concentration of NH4 increases. These all are advantageous to vanadium precipitation in the solution (Zhang, and Shen, 1991; Wang et al., 2009). It was found that the lower the pH value for the precipitate formation is, the higher the contents of Mo and the impurities P, As and Si will be in the precipitate. Though the vanadium remained in the solution can be further reduced with pH value decrease, in commercial run, the practice of vanadium precipitation is by means of controlling
X. Wang et al. / Hydrometallurgy 104 (2010) 317–321
Fig. 1. Flowsheet of the process of vanadium recovery during ammonium molybdate production.
Fig. 2. Relationship of pH value and the adsorptions of vanadium and molybdenum.
Fig. 3. Adsorption curve of the resin for molybdenum.
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Table 2 Experimental results of vanadium separation and recovery in ammonium molybdate production using ion exchange method. Element
Mo
V2O5
P
As
SiO2
pH
Eluted solution, g/L Vanadium precipitate, wt.% Stood solution, g/L Purified solution, g/L Purified residue, wt.% Devanadiumized solution, g/L
87.68 10.16 86.43 78.76 0.45 75.65
9.68 72.82 0.71 0.58 0.32 0.006
6.84 0.73 6.75 0.03 15.47 0.01
0.72 0.68 0.63 0.004 1.58 0.002
5.84 5.12 5.11 0.11 12.63 0.01
9.55 – 7.42 8.10 – 6.75
Fig. 4. Relationship of standing time and vanadium remained in the eluted solution.
Fig. 5. Influence of pH value on vanadium precipitation in the eluted solution.
the peak-solution volume to adjust the pH value about 8.0 and prolonging the standing time to over 48 h. In the resin elution, with peak-solution volume increase, the pH value rises in the solution. From Tables 1 and 2, it can be seen that some of impurities P, As and Si were adsorbed along with the molybdenum from the feed liquid and then came into the eluted solution. To remove the impurities P, As and Si, the stood solution was purified with MgCl2 under the pH value range of 8.0–9.0 at 60–80 °C for about 2 h. The purification results are listed in Table 2. Table 2 shows that, after purification, the impurities P, As and Si were almost removed from the raw ammonium molybdate solution, while the vanadium needs to be further separated. The vanadium (V) in the solution containing about
0.58 g/L V2O5 (lgCV (total) = − 2.19) in pH value range 7.0–8.0 is mostly in the form of V3O3− (Zhang, and Shen, 1991) and, the 9 molybdenum (VI) in the solution is in the form of MOO2− 4 (Zhang and Zhao, 2005; Baes and Mesmer, 1976). The charges contained in V3O3− 9 are higher than that in MOO2− 4 , which made the strong base anion exchange resin D296 adsorb V3O3− 9 preferentially, so vanadium can be removed from the ammonium molybdate solution with ion exchange (Qian, 1984; Dean, 1985). By adsorption with the resin D296 in pH value about 7.0, the concentration of vanadium was less than 0.008 g/L V2O5 in the effluent collected till the breakthrough point 0.02 g/L V2O5 (Hu et al., 2009), which can be used to be produced high-quality ammonium molybdate because the impurities P, As and Si were further removed from the solution during ion exchange, see Table 2. The loaded vanadium resin was eluted and regenerated using HCl 6 mol/L because the vanadium can be turned into VO+ 2 completely when the pH value is less than 1.0 (Zhang, and Shen, 1991). Then the eluted solution was returned to the working operation of sodium molybdate solution pH value adjustment, see Fig. 1. Thus the vanadium was effectively separated and recovered in the process. The vanadium precipitate used to produce vanadium pentoxide was obtained from Qinghe Huanqiu Chemical Plant because the vanadium precipitate formed in the experimental solution is too little to be used. Table 3 is the composition of the industrial vanadium precipitate, which was offered by the Plant. From Table 3, it can be deduced that the vanadium in the precipitate is in the form of ammonium isopoly-vanadate because the V2O5 content is about 77.77% in pure ammonium metavanadate. Table 3 shows that there are not only acidic-impurities (Mo, P, As, Si) but also basic-impurities (Al, Na, and Ca) in the precipitate. The basic-impurities can be dissolved in diluted HCl solution and, mostly of the acidic-impurities can be dissolved in ammonia solution, while the solubility of V(V) in diluted HCl solution or in ammonia solution is very limited. To remove the impurities, the precipitate was first grinded to less 75 μm and then washed with HCl 0.5 mol/L in liquid/ solid ratio 2:1 mL/g under stirring at room temperature for 3 h. After filtering, the precipitate was washed with ammonia liquor in liquid/ solid ratio 1:1 mL/g under stirring at 60 °C in pH value 9.5 for 1 h. The composition of the treated precipitate is listed in Table 3. From Table 3 it can be deduced that the ammonium isopoly-vanadate in the precipitate has been completely turned into ammonium metavanadate. By roasting the treated precipitate at 500 °C for 2 h, the product of V2O5 with the purity 99.12% was obtained.
4. Conclusion For ammonium molybdate production, vanadium is a harmful substance as well as a valuable constituent. The vanadium can be effectively concentrated along with the molybdenum from sodium molybdate solution by adsorbing with weak base anion exchange resin in the pH range of 2.5–3.5 and eluting with ammonia liquor. Most of the vanadium in the eluted solution can be precipitated by adjusting the pH value to 7.0–8.0 and standing for 24–48 h. The vanadium remained in the eluted solution can be further separated by adsorption with strong base anion exchange resin in pH value about 7.0. By washing with hydrochloric acid and then ammonia solution, the treated vanadium precipitate can be used to produce V2O5 expediently.
Table 3 Experimental results of industrial vanadium precipitate washed with hydrochloric acid and ammonia solution, wt.%. Element
Na
Al
SiO2
S
P
Ca
V2O5
As
Mo
Cl
Raw precipitate Treated precipitate
0.031 0.001
0.060 0.001
0.31 0.11
0.008 0.001
0.68 0.002
0.023 0.001
80.03 77.02
0.70 0.003
5.75 0.06
0.23 0.02
X. Wang et al. / Hydrometallurgy 104 (2010) 317–321
References Baes, Ch.F., Mesmer, R.E., 1976. The Hydrolysis of Cations. Wiley, New York. Biswas, R.K., Wakihara, M., Taniguchi, M., 1985. Recovery of vanadium and molybdenum from heavy oil desulphurization waste catalyst. Hydrometallurgy 14, 219–230. Chemistry department, Hangzhou University, 1982. Chemical Analysis. Analytical Chemistry Handbook, Part II). Chemical Industry Press, Beijing. (in Chinese). Chen, X.L., Xiao, L.S., Xu, J., Wang, J.S., 2004. A study on recovering vanadium and molybdenum from spent catalyst. Min. Metal. Eng. 24, 47–49 (In Chinese). Dean, J.A., 1985. Lange's Chemistry Handbooked.13. McGraw-Hill, Inc. Henry, P., Van Lierde, A., 1998. Selective separation of vanadium from molybdenum by electrochemical ion exchange. Hydrometallurgy 48, 73–81. Hirai, T., Komasawa, I., 1993. Electro-reductive stripping of vanadium in solvent extraction process for separation of vanadium and molybdenum using tri-n-octylmethylammonium chloride. Hydrometallurgy 33, 73–82. Hu, J.F., Zhu, Y., Hu, H., 2006. Comprehensive recovery of vanadium, molybdenum and nickel from dead catalyst. Chinese J. R. Met. 30, 711–714 (In Chinese). Hu, J., Wang, X.W., Xiao, L.S., Song, S.R., Zhang, B.Q., 2009. Removal of vanadium from molybdate solution by ion exchange. Hydrometallurgy 95, 203–206. Komasawa, I., Hosoba, H., Kurokawa, N., Otake, T., 1987. Extraction of molybdenum and vanadium from hydrochloric acid by tri-n-butyl phosphate in various diluent solutions. J. Chem. Eng. Jpn 20, 176–182. Li, Q.G., Zeng, L., Xiao, L.S., Yang, Y.N., Zhang, Q.X., 2009. Completely removing vanadium from ammonium molybdate solution using chelating ion exchange resins. Hydrometallurgy 98, 287–290. Luo, L., Miyazaki, T., Shibayama, A., Yen, W., Fujita, T., Shindo, O., Katai, A., 2004. Recovery of tungsten and vanadium from tungsten alloy scrap. Hydrometallurgy. 74, 1–8.
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Neková , P., Schrötterová, D., 2000. Extraction of V(V), Mo(VI) and W(VI) polynuclear species by primene JMT. Chem. Eng. J. 79, 229–233. Qian, T.B., 1984. Applied Technology of Ion Exchange Reagent. Tianjin Science and Technology Press, Tianjin, p. 43 (In Chinese). Shi, Y.F., Wang, H.B., 2004. Separation of molybdenum and vanadium from spent catalysts. China Mo. Ind. 28, 39–41 (In Chinese). Wang, M.Y., Wang, X.W., 2010. Extraction of molybdenum and nickel from carbonaceous shale by oxidation roasting, sulphation roasting and water leaching. Hydrometallurgy 102, 50–54. Wang, X.W., Xiao, L.S., Gong, B.F., Li, Q.G., 2006. A techniques for producing ammonium molybdate with high impurity molybdenum–iron alloy. Chinese Patent No. ZL 200610031634.9. Wang, X.W., Xiao, L.S., Liu, W.L., 2007. Study on oxidizing roasting of high impurity ferromolybdenum. Chinese J. R. Met. 31 (3), 391–394 (In Chinese). Wang, X.W., Lui, W.L., Zhang, G.Q., Wang, M.Y., Hu, J., 2009. Recovery of vanadium by nanofiltration from the leaching solution of stone coal roasted with sodium chloride. Chin. J. Process Eng. 9, 289–292. Zhang, Q.L., Shen, P.W., 1991. Titanium, Vanadium and Chromium. Vol. 8 of Inorganic Chemistry Series. Science Press, Beijing, p. 238 (In Chinese). Zhang, Q.X., Zhao, Q.S., 2005. Metallurgy of Tungsten and Molybdenum. Metallurgy Industry Press, Beijing, p. 239 (In Chinese). Zhang, P.W., Inoue, K., Yoshizuka, K., Tsuyama, H., 1996. Extraction and selective stripping of molybdenum(VI) and vanadium(IV) from sulfuric acid solution containing aluminum(III), cobalt( II), nickel(II) and iron(III) by LIX 63 in Exxsol D80. Hydrometallurgy 41, 45–53.
Contents lists available at ScienceDirect
Hydrometallurgy j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / h yd r o m e t
Short communication
Recovery of vanadium during ammonium molybdate production using ion exchange Xuewen Wang ⁎, Mingyu Wang, Lihua Shi, Jian Hu, Peng Qiao School of Metallurgical Science and Engineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 27 April 2010 Received in revised form 19 June 2010 Accepted 20 June 2010 Available online 26 June 2010 Keywords: Molybdenum Vanadium Separation Recovery Ion exchange
a b s t r a c t The recovery of vanadium in ammonium molybdate production with raw sodium molybdate solution was studied. Experimental results showed that the vanadium and some of impurities P, As and Si can be adsorbed along with the molybdenum from the feed liquid by the weak base resin D314 in the pH range of 2.5–3.5 and then they can be eluted from the loaded resin with ammonia liquor. The vanadium can partially naturalprecipitate from the eluted solution. The lower the pH value is and, the longer the standing time is, the less the vanadium remained in the solution will be. Standing for 24 h in pH value 6.9, the vanadium in the solution was reduced to 0.51 g/L V2O5. It was found that the precipitate is ammonium isopoly-vanadate and it is impure. By washing the precipitate with hydrochloric acid and ammonia solution sequentially and then roasting at 500 °C for 2 h, the product of V2O5 with the purity 99.12% was obtained. The impurities P, As and Si in the stood solution were removed by purifying with MgCl2 under the pH value range of 8.0–9.0 at 60–80 °C for about 2 h, while the removal of the vanadium in the solution was performed by adsorbing with the strong base resin D296 in pH value about 7.0. The devanadiumized solution can be used to produce high-quality ammonium molybdate. The loaded vanadium resin was eluted with HCl 6 mol/L and, the eluted solution was returned to adjust the sodium molybdate solution pH value. The vanadium can be effectively separated and recovered in the process. © 2010 Elsevier B.V. All rights reserved.
1. Introdution Due to numerous co-properties in chemistry of molybdenum and vanadium, it is relatively more difficult to separate and recover vanadium from molybdate solution. In ammonium molybdate production, if the average vanadium concentration is more than 0.01 g/L V2O5 in the ammonium molybdate solution, the ammonium molybdate crystal formed by adding nitric acid in the solution will be yellow, and the content of vanadium is commonly above 0.0015% in the yellow crystal. The color is not natural for the molybdenum oxide obtained by calcining the yellow crystal at about 350 °C. The molybdate solution which containing vanadium, commonly referred to the leaching solutions of dead catalyst from petroleum-refining industries for hydrogenation processes, Ni–Mo ore, high impurity Ni– Mo–Fe alloy and so on, has become one of the principal raw materials for the production of ammonium molybdate in China (Shi and Wang, 2004; Hu et al., 2006; Wang and Wang, 2010; Wang et al., 2007). In the leaching solution, the vanadium (V) is in the form of VO− 3 at the pH value over 8.0 and, the VO− 3 changes into isopoly-vanadic acid anion with the pH value decrease from 8.0 to 2.5, then the isopoly-
⁎ Corresponding author. E-mail address: [email protected] (X. Wang). 0304-386X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.hydromet.2010.06.012
vanadic acid anion transforms into VO+ 2 when the pH value is less than 2.5 (Zhang, and Shen, 1991). The molybdenum (VI) in the solution is in 2− the form of MOO2− 4 at the pH value over 6.5 and, the MOO4 changes into isopoly-molybdic acid anion with the pH value decrease from 6.5 to 2.5, then the isopoly-molybdic acid anion partial transforms into MoO2+ 2 when the pH value is less than 2.5 (Zhang and Zhao, 2005; Baes and Mesmer, 1976). Therefore, the molybdenum and the vanadium in the feed solution can be simultaneously adsorbed by weak base resin at the pH range from 2.5 to 6.5 and, after eluting the loaded resin with ammonia solution, the ammonium molybdate solution containing vanadium can be obtained (Hu et al., 2009). To produce pure ammonium molybdate, many methods, such as ammoniate precipitation (Chen et al., 2004; Biswas et al., 1985; Luo et al., 2004), solvent extraction (Neková and Schrötterová, 2000; Zhang et al., 1996; Komasawa et al., 1987) and ion exchange (Hu et al., 2009; Henry and Van Lierde, 1998; Hirai and Komasawa, 1993; Li et al., 2009), have been used to remove vanadium from molybdate solution, while the recovery of vanadium was commonly overlooked, which resulted in not only vanadium resource uneconomicalness but also environmental pollution in ammonium molybdate production. The present investigation deals with the application of ammoniate precipitation and ion exchange to separate vanadium from ammonium molybdate solution and to obtain purified ammonium metavanadate by using hydrochloric acid and ammonia solution to decontaminate for the vanadium precipitate.
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was decontaminated with hydrochloric acid and ammonia solution and then roasted to obtain vanadium pentoxide.
2. Experimental methods 2.1. Materials and analysis
3. Results and discussion The sodium molybdate solution used to produce ammonium molybdate was obtained from Qinghe Huanqiu Chemical Plant, which was produced by roasting high impurity ferromolybdenum powder with sodium carbonate in air and leaching the calcined powder with water (Wang et al., 2006). The composition of the solution was shown in Table 1. Hydrochloric acid, ammonia liquor, magnesium chloride, distilled water, weak base anion exchange resin D314 and strong base anion exchange resin D296 were used in the experiments. The resins were obtained from Hangzhou Zhengguang Chemical Company. Molybdenum was determined with ammonium thiocyanate colorimetry by spectrophotometer, vanadium was titrated with ammonium ferrous sulfate (Chemistry Department, 1982). Arsenic, phosphorus and silicon was determined by chemical methods and inductively coupled plasma emission spectroscopy (ICP) with a PS-6 PLASMA SPECTROVAC, BAIRD (USA). The pH was determined with ORION-230A which was made in USA, the degree of accuracy is 0.01.
Fig. 2 is the relationship of feed liquid pH value and Mo operating adsorption capacity of the resin D314 and the V concentration in the effluent at the breakthrough point of 0.1 g/L Mo. Fig. 2 shows that the resin adsorption capacity for molybdenum increases with the pH value decrease from 5.23 to 2.72, then the adsorption capacity decreases with pH value decrease. The resin has a maximal operating adsorption capacity of 142.8 g/L at pH 2.72. The adsorption capacity is 100.3 g/L at pH 1.72, which is close to the adsorption capacity 107.6 g/L at pH 3.57. To outward seeming, this is contrary to the form of the molybdenum (VI) existing in the solution. Fig. 3 is the adsorption curve of the resin D314 for molybdenum at pH 1.72. Fig. 3 shows that the pH value in the effluent is higher than that in the feed liquid, which indicates that the adsorption can promote MOO2− 4 condensation (Zhang and Zhao, 2005).
2.2. Experimental procedure
2 RCl + 2H + 2MoO4
The resins were respectively first soaked in distilled water for 24 h, and then alternately soaked in NaOH 2 mol/L and HCl 2 mol/L for 2 h, repeated three times as this way, at last activated with HCl 2 mol/L and rinsed with distilled water before use. Trials for the sodium molybdate solution ion exchange with the resin D314 were carried out in a glass column ϕ2.0 × 40 cm which operated with the pH value adjusted solution at the temperature 25 ± 0.5 °C. Forty (40) milliters of the resin was wet-packed into the glass column. The operation was performed by downstream flow at a constant flow rate of 40 ml/h. Samples were collected periodically from the column effluent and analyzed to determine vanadium and molybdenum content. The loaded resin was eluted with NH3·H2O 6 mol/L and regenerated with HCl 2 mol/L by downstream flow at the flow rate of 40–80 ml/h. The separation of vanadium from ammonium molybdate solution with the resin D296 was carried out in a glass column ϕ2.0 × 32 cm which operated with the purified solution at the temperature 25± 0.5 °C. Thirty (30) milliliters of the resin was wet-packed into the glass column. The operation was performed by downstream flow at a constant flow rate of 30 ml/h. Samples were collected periodically from the column effluent and analyzed to determine vanadium and molybdenum content. The loaded resin was eluted and regenerated with HCl 6 mol/L by downstream flow at a constant flow rate of 30 ml/h. The separation and recovery of vanadium in ammonium molybdate production were performed according to the flow sheet as shown in Fig. 1. To increase the resin D314 adsorption capacity, the pH value of the sodium molybdate solution was adjusted with hydrochloric acid, or the vanadium eluted solution and the ammonium molybdate crystal mother liquor (see Fig. 1). After adsorption, the molybdenum and the vanadium loaded on the resin was eluted with ammonia liquor. The pH value of the eluted solution was adjusted with hydrochloric acid to make the vanadium precipitated. To remove the impurities P, As and Si, the eluted solution was purified with MgCl2. The vanadium remained in the purified solution was further removed by adsorbing with the resin D296. The vanadium loaded on the resin was eluted with hydrochloric acid. The vanadium precipitate Table 1 Composition of the solution obtained by leaching the calcined ferromolybdenum powder with water, g/L. Mo
V2O5
P
As
SiO2
pH
22.42
2.48
5.21
0.27
7.28
9.76
3.1. Vanadium adsorption
P
þ
P
þ
2−
= R4 Mo4 O13 + 2Cl
P
þ
2−
+ MoO4
2−
4RCl + 2H + 2Mo2 O7 6RCl + 2H + 3Mo2 O7
P
−
+ H2 O
ð1Þ
−
ð2Þ
= R2 Mo2 O7 + 2Cl P
2−
+ H2 O
P
−
= R6 Mo7 O24 + 6Cl
+ H2 O ð3Þ
From Fig. 2 it can be seen that Mo adsorption capacity decreases markedly when the feed liquid pH value is higher than 3.5, while the V concentration in the effluent increases evidently if the feed liquid pH value is less than 2.5, which indicates the optimal pH value range for the resin adsorbing molybdenum and vanadium from the solution should be from about 2.5 to 3.5. 3.2. Vanadium separation and recovery The molybdenum and the vanadium can be eluted from the loaded weak base resin with ammonia liquor. The composition of the eluted solution is listed in Table 2. It was found that the vanadium can partially natural-precipitate from the eluted solution and, the precipitation depends on the pH value as well as the standing time. Ammonium vanadate precipitate can be formed in the solution containing vanadium (V) by adding ammonium salt (Zhang, and Shen, 1991). In fact, the eluted solution is the mixed solution of ammonium molybdate, ammonium vanadate and ammonium chloride. Fig. 4 is relationship of the standing time and the vanadium concentration in the solution, which was adjusted the pH value from 9.55 to 7.42 with HCl 6 mol/L at room temperature. Fig. 4 shows that vanadium precipitation in the solution is close to balance after standing for 24 h at pH 7.42. The compositions of the vanadium precipitate and the stood solution after standing for 24 h are listed in Table 2 as well. Fig. 5 is the vanadium concentrations in the solution in different pH value after standing for 24 h at room temperature. From Fig. 5, it can be seen that, in the pH value range of 9.5–6.9, the lower the pH value is, the less the vanadium remained in the solution will be. After standing for 24 h in pH 6.9, the V2O5 in the solution was reduced to 0.51 g/L. With HCl addition, the pH value decreases, the form of the vanadium existing in 4+ the solution becomes HV2O2+ 7 and V4O12 (Zhang, and Shen, 1991) and, + the concentration of NH4 increases. These all are advantageous to vanadium precipitation in the solution (Zhang, and Shen, 1991; Wang et al., 2009). It was found that the lower the pH value for the precipitate formation is, the higher the contents of Mo and the impurities P, As and Si will be in the precipitate. Though the vanadium remained in the solution can be further reduced with pH value decrease, in commercial run, the practice of vanadium precipitation is by means of controlling
X. Wang et al. / Hydrometallurgy 104 (2010) 317–321
Fig. 1. Flowsheet of the process of vanadium recovery during ammonium molybdate production.
Fig. 2. Relationship of pH value and the adsorptions of vanadium and molybdenum.
Fig. 3. Adsorption curve of the resin for molybdenum.
319
320
X. Wang et al. / Hydrometallurgy 104 (2010) 317–321
Table 2 Experimental results of vanadium separation and recovery in ammonium molybdate production using ion exchange method. Element
Mo
V2O5
P
As
SiO2
pH
Eluted solution, g/L Vanadium precipitate, wt.% Stood solution, g/L Purified solution, g/L Purified residue, wt.% Devanadiumized solution, g/L
87.68 10.16 86.43 78.76 0.45 75.65
9.68 72.82 0.71 0.58 0.32 0.006
6.84 0.73 6.75 0.03 15.47 0.01
0.72 0.68 0.63 0.004 1.58 0.002
5.84 5.12 5.11 0.11 12.63 0.01
9.55 – 7.42 8.10 – 6.75
Fig. 4. Relationship of standing time and vanadium remained in the eluted solution.
Fig. 5. Influence of pH value on vanadium precipitation in the eluted solution.
the peak-solution volume to adjust the pH value about 8.0 and prolonging the standing time to over 48 h. In the resin elution, with peak-solution volume increase, the pH value rises in the solution. From Tables 1 and 2, it can be seen that some of impurities P, As and Si were adsorbed along with the molybdenum from the feed liquid and then came into the eluted solution. To remove the impurities P, As and Si, the stood solution was purified with MgCl2 under the pH value range of 8.0–9.0 at 60–80 °C for about 2 h. The purification results are listed in Table 2. Table 2 shows that, after purification, the impurities P, As and Si were almost removed from the raw ammonium molybdate solution, while the vanadium needs to be further separated. The vanadium (V) in the solution containing about
0.58 g/L V2O5 (lgCV (total) = − 2.19) in pH value range 7.0–8.0 is mostly in the form of V3O3− (Zhang, and Shen, 1991) and, the 9 molybdenum (VI) in the solution is in the form of MOO2− 4 (Zhang and Zhao, 2005; Baes and Mesmer, 1976). The charges contained in V3O3− 9 are higher than that in MOO2− 4 , which made the strong base anion exchange resin D296 adsorb V3O3− 9 preferentially, so vanadium can be removed from the ammonium molybdate solution with ion exchange (Qian, 1984; Dean, 1985). By adsorption with the resin D296 in pH value about 7.0, the concentration of vanadium was less than 0.008 g/L V2O5 in the effluent collected till the breakthrough point 0.02 g/L V2O5 (Hu et al., 2009), which can be used to be produced high-quality ammonium molybdate because the impurities P, As and Si were further removed from the solution during ion exchange, see Table 2. The loaded vanadium resin was eluted and regenerated using HCl 6 mol/L because the vanadium can be turned into VO+ 2 completely when the pH value is less than 1.0 (Zhang, and Shen, 1991). Then the eluted solution was returned to the working operation of sodium molybdate solution pH value adjustment, see Fig. 1. Thus the vanadium was effectively separated and recovered in the process. The vanadium precipitate used to produce vanadium pentoxide was obtained from Qinghe Huanqiu Chemical Plant because the vanadium precipitate formed in the experimental solution is too little to be used. Table 3 is the composition of the industrial vanadium precipitate, which was offered by the Plant. From Table 3, it can be deduced that the vanadium in the precipitate is in the form of ammonium isopoly-vanadate because the V2O5 content is about 77.77% in pure ammonium metavanadate. Table 3 shows that there are not only acidic-impurities (Mo, P, As, Si) but also basic-impurities (Al, Na, and Ca) in the precipitate. The basic-impurities can be dissolved in diluted HCl solution and, mostly of the acidic-impurities can be dissolved in ammonia solution, while the solubility of V(V) in diluted HCl solution or in ammonia solution is very limited. To remove the impurities, the precipitate was first grinded to less 75 μm and then washed with HCl 0.5 mol/L in liquid/ solid ratio 2:1 mL/g under stirring at room temperature for 3 h. After filtering, the precipitate was washed with ammonia liquor in liquid/ solid ratio 1:1 mL/g under stirring at 60 °C in pH value 9.5 for 1 h. The composition of the treated precipitate is listed in Table 3. From Table 3 it can be deduced that the ammonium isopoly-vanadate in the precipitate has been completely turned into ammonium metavanadate. By roasting the treated precipitate at 500 °C for 2 h, the product of V2O5 with the purity 99.12% was obtained.
4. Conclusion For ammonium molybdate production, vanadium is a harmful substance as well as a valuable constituent. The vanadium can be effectively concentrated along with the molybdenum from sodium molybdate solution by adsorbing with weak base anion exchange resin in the pH range of 2.5–3.5 and eluting with ammonia liquor. Most of the vanadium in the eluted solution can be precipitated by adjusting the pH value to 7.0–8.0 and standing for 24–48 h. The vanadium remained in the eluted solution can be further separated by adsorption with strong base anion exchange resin in pH value about 7.0. By washing with hydrochloric acid and then ammonia solution, the treated vanadium precipitate can be used to produce V2O5 expediently.
Table 3 Experimental results of industrial vanadium precipitate washed with hydrochloric acid and ammonia solution, wt.%. Element
Na
Al
SiO2
S
P
Ca
V2O5
As
Mo
Cl
Raw precipitate Treated precipitate
0.031 0.001
0.060 0.001
0.31 0.11
0.008 0.001
0.68 0.002
0.023 0.001
80.03 77.02
0.70 0.003
5.75 0.06
0.23 0.02
X. Wang et al. / Hydrometallurgy 104 (2010) 317–321
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